Heavy Metals

Formation of Heavy Metal Pollution

Heavy metals are naturally occurring elements in Earth's crust. Some heavy metals are essential to maintain health and metabolism of the body. Heavy metals enter our bodies through food, water, or air.

Ingesting very high concentrations of heavy metals can lead to toxicity and associated health problems.

Natural phenomena, such as weathering and volcanic eruptions, can contribute to the formation of heavy metal pollution. Alternatively, heavy metal pollution can result from anthropogenic sources, such as:

• Industrial waste

• Mining and smelting processes

• Agricultural use of metals

• Processing plants

• Burning fossil fuels

• Nuclear power stations

Characteristics of Heavy Metals

As their name implies, heavy metals are dense elements. Heaviness is suggested to be associated with toxicity.

Other characteristics include:

• Lustre: the surface of heavy metals have a gentle sheen.

• Ductility: heavy metals can undergo changes in their physical form without breaking.

• Malleability: the shape of heavy metals can be easily distorted under compression.

• Conductivity: heavy metals can effectively conduct heat and electricity.

Importance of Heavy Metals

In trace amounts, heavy metals have important biochemical and physiological functions in living organisms. Copper and zinc in particular are very useful in the body.

Heavy metals are also important due to their tendency to bioaccumulate.

Chemicals accumulate in living organisms when they are taken up and stored faster than they can be metabolised or excreted.

Bioaccumulation is associated with biomagnification.

The bioaccumulation and biomagnification tendencies of toxic heavy metals can cause health issues in living organisms, including humans.

Examples of Heavy Metals

Now, we're going to look at some common heavy metals, their anthropogenic sources, and the health problems that they can cause in humans.

Dispersal and Degradation of Heavy Metals

Heavy metal pollution is typically dispersed (spread over a wide area) through wind, water, and soil.

Heavy metals are non-biodegradable, so they continue to persist in the environment. Thus, heavy metal pollution requires remediation.

Monitoring Heavy Metal Pollution

In the UK, heavy metal pollution is studied using a monitoring network, which consists of 15 rural sites around the UK. It measures the deposition and background concentrations of heavy metals, by analysing rainwater and atmospheric particulates. The metal concentrations are combined with meteorological data to calculate deposition, and build deposition maps of the UK.

This monitoring network is used to predict heavy metal mobility, and inform monitoring programmes. The, vulnerable members of the public are identified and informed about the risk of heavy metal pollution.

Controlling Heavy Metals

We've learned that heavy metal pollution is non-biodegradable and can lead to severe health problems if ingested in large amounts. So, it's important to limit heavy metal pollution.

Phytoremediation

It's a form of bioremediation, suitable for a variety of contaminants, including:

• Metals

• Pesticides

• Explosives

• Oil

Fibre crops are grown in soils contaminated by heavy metal ions.

As they grow, fibre crops extract the heavy metal ions from the soils by storing them in their roots, stems, or leaves. They can convert the ions into less harmful chemicals within the plant or root zone, where they are released into the air as gases, or transferred to soil microbes who break them down.

Phytoremediation is a slow, but effective process. However, phytoremediation techniques work best where contaminant levels are low. Otherwise, high concentrations may limit plant growth.

Adsorption Using Polymers

Polymers are widely used to remove heavy metal ions from wastewater. The metal ions adhere to the polymer, which has a high surface area.

The adsorption process is cheap, highly available, and environmentally friendly. Polymers have a high removal capacity, and cannot be damaged by high concentrations of heavy metal ions.

Heavy Metal Stabilisation using Polymer Technology

EcoBond® is a chemical additive that converts heavy metals in soils and sediments to insoluble minerals. Thus, it permanently stabilises the harmful ions, limiting leaching and its associated ecological problems. EcoBond® products are made of hybrid elastimeric bond (HEB) polymers. It works by drawing in moisture, eliminating off-gassing.

Agricultural Control Techniques

A common cause of heavy metals in agricultural soil is agrochemicals and inorganic fertilisers. This can be limited by:

• Growing plants with lower transfer factors (preventing metals from spreading into edible parts of the crop)

• Applying organic soil amendments to decrease metal accumulation

• Crop rotation

• Planting crops for phytoremediation

I hope that this article has explained heavy metals for you. Remember that they are dense, toxic metals that can cause a variety of health problems. Control strategies for heavy metal pollution include phytoremediation and adsorption using polymers.

^{1. Nixalite of America Inc., Eco Bond, 2013}

^{2. UK Centre for Ecology & Hydrology, Introduction to Heavy Metal Monitoring, 2022}

^{3. World Health Organization, Lead Poisoning, 2022}